Mineral fiber mat and process of making same



Dec'. 29, 1953 'r. E. PHlLIPPS MINERAL FIBER MATS AND PROCESS OF MAKING SAME Filed July 19, 195] 5 INVENTOR. @zgj 1mm, E. PkiZi a Patented Dec. 29, 1953 MINERAL FIBER MAT AND PROCESS OF MAKING SAME Thomas E. Philipps, Newark, Ohio, assignor to Owens-Corning Fiber poration of Delaware glas Corporation, a cor- Application July 19, 1951, Serial No. 237,618

This invention relates to the treatment of mineral fibers and more particularly glass fibers to produce a mat adapted particularly for use as a separator or retainer mat in storage batteries.

Ordinarily, in the making of mineral fiber mats of the present type, the fibers are deposited on a slowly moving conveyor to form a web or mat having a thickness varying from about a few thousandths of an inch to one quarter of an inch. Binding material is usually applied to the fibers, either before or after they are deposited on the conveyor, as by spraying or dipping, and, subsequently, this binding material is heated to be cured, fused, or otherwise set to a form in which the fibers are firmly bound in the desired relation. When the mat is used as a retainer mat or separator in electric storage batteries, it is desired to have the binder resistant to the battery acids and unaffected by the battery reactions.

Heretofore, a number of materials have been employed to bond the fibers, but these materials have not completely satisfied the requirements where the mats are for storage battery use. The components of the binder must be resistant to acid. No component can contain chlorine since the resulting formation of hydrochloric acid attacks the battery plates. This precludes the use of vinyl chlorides, chlorinated rubber, and the like. Also, animal glues are usually leached with hydrochloric acid during their processing so that they often contain chlorides and for the same reason are objectionable. Nor should acetates or any organic acid derivative, acid anhydride, or other acid forming compound be present in any of the ingredients. 7 r M In addition, practice has indicated that the presence of free nitrogen is detrimental to the performance of a battery. Consequently, casein,

albumen, and compounds which may, under some conditions, lose their nitrogen as through decomposition, cannot be used. a

An object of the invention is to produce an improved bonded mineral wool adapted particularly for battery use which not only has increased resistance to battery acids, but does not militate against the performance of the battery.

In accordance with this invention, a binder composed principally of polystyrene or acrylic resin such as me'thacrylate is employed. Poly-- styreneis particularly resistant to attack by 8111- phuri c-acid and also has excellent electrical properties and is resistantto moisture. It is found that the molding powder grade, that is, medium 'nw wu er w g t r n. is most desirable.

12 Claims. (Cl. 154-101) 2 the polymer range being between 65,000 and 85,000 molecular weight.

With respect to the acrylic resins, those particularly contemplated have this monomeric structure:

1 n coon wherein R is a radical selected from the class consisting of hydrogen and methyl, and R is an alkyl radical selected from the class consisting of methyl, ethyl, propyl, isopropyl, butyl and isobutyl.

Of these acrylic resins, methyl acrylate and methyl methacrylate (sometimes referred to for convenience simply as methacrylate) are preferable. It is often desirable to plasticize these resins in order to use lower baking temperatures or provide a more flexible product. For this purpose many of the conventional plasticizers may be used as will be apparent to those skilled in the art. However, the phthalates such as dibutyl phthalate, diethyl phthalate, and dimethyl phthalate are recommended especially when the mineral fiber mat is to be used in storage batteries.

In the present specification and claims, forms of the term plasticizer are taken to include other acrylic resins of the described monomeric structure which also may be applicable for that purpose. As an instance, butyl acrylate or butyl methacrylate, which are softer acrylic resins, are well suited for the plasticizing of methyl acrylate or methyl methacrylate.

The amount of plasticizer employed is not critical and largely dependent on the results desired, Ordinarily, the amount of plasitcizer may range from 15 per cent to 50 per cent by weight of the resin to be plasticized.

The molecular weight of the acrylic resins used may vary widely since it is contemplated and required only that the resins fuse upon exposure to elevated temperatures as compared to room temperatures, fiow along fibers to form a coating as more fully described hereafter, and then congeal as upon cooling. In practice, themolecular weights preferred are those of the molding pow-' resins of these molecular weights do not fuse too readily nor too slowly. For example, resins of such molecular weights flow well at about 250 F. to 475 F. e

Particularly in the case of methyl methacry- 3 late, a resin is contemplated having a polymeric growth of such degree as to provide a specific gravity of about 1.16 to 1.20 in the resin, a molding temperature of about 285 F. to 340 F., or an injection temperature of about 325 F. to 475 F.,

as these steps are today practiced in the art.

The lower molecular weight resins of these types have insuflicient strength for the purpose of the invention. Accordingly, polystyrene having a molecular weight below 65,000 and acrylic resins which are substantially deformable at room temperatures are not preferred. On the other hand, solutions of these higher molecular weight resins, that is, polystyrene resins having a molecular weight over about 85,000 and acrylic resins which fuse substantially above 475 F., are not readily usable because of the dangers and high costs incident to the use of solvents. For this reason the resin binder is applied in the form of an aqueous emulsion or dispersion. The use of dispersions are attended with great difiiculty, however, in that as the vehicle is evaporated during the heat treatment of the binder, the resin is deposited on the fibers as separate particles of hardened resin which are devoid of any adhesiveness. As a result, the fibers of the mat fluif up and otherwise move from desired compact relation where the vehicle evaporates, and subsequent fusion of the binder particles by the heat treatment is incapable of binding the fibers into the required relation in the mat. The mats are, as a consequence, poorly bonded, fuzzy, and have poor strength.

It is another object of the invention to provide a process utilizing resin dispersions for binding glass fibers in a mat by which a compact, well bonded, product may be obtained.

In accordance with a second aspect of the invention, the integrity of the mat is initially maintained by one binder until subsequently another binder which is normally nonadhesive but is rendered adhesive by changed temperature conditions, replaces the preliminary binder, the final binder preferably having certain properties rendering it particularly useful for use in storage batteries.

The resin constituent of the binder, preferably polystyrene of the specified molecular weight, or methacrylate or any of the other disclosed acrylic resins having similar physical characteristics, is mixed with gelatin in a ratio of about 15 parts gelatin to 85 parts polystyrene or methacrylate although other proportions ranging from about partsgelatin up to 25 parts gelatin with '75 to 90 parts of polystyrene or methacrylate may be used. The polystyrene or other resin is preferably polymerized in an aqueous emulsion .or dispersion so that in order to produce the binder all that is necessary is to add the gelatin tothe emulsion or dispersion. In some processes, the gelatin may be added to theoriginal mixture to operate as the dispersing agent. In. any event, the gelatin adds to the stability of the suspension.

Specific examples of binder formulations follow:

Example I 12.5 pounds-Methyl methacrylate emulsion of 40% solids content and molecular weight of the molding powder grade.

6 pounds-Dibutyl phthalate. emulsion (28%- solids content).

0.2 pound-Gelatin of commercial. grade h10:

rine-free).

47.8 gallons-Distilled water.-

lons by adding the remainder of the water. The

agitation should be sufficient only to mix thoroughly .theingredients.

Example II 17.0 pounds-Methyl acrylate emulsion of 25% .resin solids and molecular weight of the molding powder grade.

12.0 pounds-Butyl acrylate emulsion of 20% resin solids.

0.2 pound-Gelatin of commercial grade (chlorine-free).

46.5 gallons-Water The preparation of this formulation is similar to steps set forth for Example 1 beginning with the addition of the gelatin in about one-half of the amount of water.

The method of applying the emulsion or mixture to the mineral fibers may be similar to any of those presently in use. The mixture may be sprayed onto the fibers as they build up into mat formation, or the mat may be saturated by dipping or other suitable means. After the fibers are properly coated, the mat is heated to cause the binding agent to be converted to its final set, in the present case, to be fused. A baking tel perature of 250 to 450 F. for three to twenty minutes, suffices to drive off the volatiles and effect the desired fusion. A somewhat higher temperature, about 475 F., may be used in the case of the acrylic resins. The gelatin retains the fibers in place until the fusion of the polystyrene or acrylic resin takes place and also during the time the diluent is reduced to such an extent that it no longer causes the fibers to cling to each other. The styrene or acrylic polymer preferably usedhas a lower fusion temperature as a result of its plasticization by the dibutyl phthalate or other plasticizers, but unplasticized resins may, of course, be used by resorting to higherbakmg temperatures. The binder of this invention makes use of the adhesiveness of gelatin in solution during the timethe vehicle for the resin is being removed. The temperature of the bake is in the softening range of the styrene or acrylic polymer, and at this point the resin fuses to afford a binder for retaining the fibers together. The gelatin is apparently sufficiently incorporated in or mixed with the styrene or acrylic resins, or its binding effect is not permanently required, because its leaching or attack by the battery acids has no noticeable effect on the mat.

One form of apparatus by which the present invention may be accomplished is disclosed in detail in Patent No. 2,306,347 to Games Slayter, dated December 22, 1942, but for purposes of illustrationreference may be hadto the accompanying drawing, inwhich-z Figural is a schematic view of apparatus which may be used in thevpresen t, process;

Figure 2 is a view on a greatly enlarged scale of the fluidbinder applied to the fibers; and

Figure 3 is a similar view illustrating the final binder stage.

Referring now to the drawings and Figure 1 in particular, the apparatus comprises a glass melting unit 5 of suitable construction adapted to discharge the molten glass in a plurality of fine streams. The flowing molten streams are engaged by a blast of steam or air from a blower 8 disposed adjacent the source of the streams and by which the streams are attenuated to fine fibers. The fibers are blown downwardly through the hood 8 onto a collecting surface which is in the form of an endless foraminous belt 9. A suction chamber I is provided beneath the belt 9 to aid in collecting the fibers in the form of a mat II in which the fibers are haphazardly arranged. The thickness of the mat is primarily controlled by regulating the speed of the belt 9. Thus, increasing the conveyor speed produces a thinner mat, and conversely, slowing the conveyor speed provides a greater thickness.

As the mat is carried from beneath the hood 8 on the conveyor 9, it is drafted into a sheet I2 by mechanism including a draft bar or idler roller I 4 and drafting rolls I5 and I6. The sheet I2 passes downwardly from the roll I4 and around the roll I 5 which is driven by any suitable mechanism. The roll I6 cooperates With the roll I5 as a pinch roll to assure uniform contact of the sheet with the roll I5. The rolls I5 and I6 serve a two-fold purpose since the roll I5 is mounted within a container I1 and is adapted for rotation partially submerged in a binder solution I8. Thus the sheet I2 is saturated with binder as it is drawn from the conveyor 9 and excess binder is squeezed out as the sheet passes between the rolls I5 and I6.

The binder impregnated sheet as it leaves the dipping tank passes through a drying and/or curing oven 20 in which a suitable baking temperature is maintained preferably by circulating heated air. The sheet is supported in the oven 20 on a traveling conveyor belt 2| and has a tensioning roll 22 cooperating therewith. The roll 22 and conveyor 2| have similar surface speeds which are slightly in excess of the drafting speed of the roll I 5. This difference in speed may be only sufiicient to prevent the sheet from wrinkling as the binder is cured. The cured sheet upon leaving the oven 20 may be rolled as at 24 or cut into sheets for storage or subsequent handling and fabrication.

Figure 2 illustrates on a gigantic scale several fibers F which represent the primary binder phase, that is, the mat after passing through the binder solution but before sufilcient heat has been applied to cause the resin to flow. Passage of the mat through the binder I8 in the tank I! produces a film on the fibers as indicated at 28. This film or residuary emulsion completely wets and covers the fibers with a uniform coating embodying the solubilized gelatin. Solid particles of resin 29 dispersed in the gelatin emulsion are adhered to the fiber surface by the fluid phase of the binder as the volatiles evaporate. The preliminary heating of the binder causes the liquid to evaporate thereby leaving a relatively solid bond of gelatin holding the fibers together. Thus fluffiness in the mat and separation of fibers is prevented until the permanent resin bond is accomplished by additionally heating the mat.

The solids content in the above stated amount have been found sufficient when melted to form a susbtantially uniform film on the fiber as indicated at 30 in Figure 3. subjecting the mat whereby the heat plasticized resin flows about the fibers and their points of contact and forms a permanent bond.

The present invention is a continuation-inpart of my application filed October 12, 1943, Serial Number 54,116, now U. S. Patent No.

. 2,566,960 wherein the combination of polystyrene and gelatin as and for the purpose here described is disclosed and claimed.

It is to be understood that modifications and variations may be effected within the spirit of the present invention as defined by the appended claims.

I claim:

1. As an article of manufacture, a mineral fibrous mat carrying a susbtantially uniform continuous film on the surface of the individual fibers, said film comprising a fused thermoplastic acrylic resin having a molecular weight of the molding powder grade and a substantial amount of gelatin incorporated therein, said acrylic resin having the following monomeric structure:

If R

1 I I coon wherein R is a radical selected from the class consisting of hydrogen and methyl, and R is an alkyl radical selected from the class consisting of methyl, ethyl, propyl, isopropyl, butyl, and isobutyl. 2. An article of manufacture as claimed in claim 1 wherein said acrylic resin has a polymeric growth conducive to ready fusing and flowing of the resin in a temperature range of about 250 F. to 475 F.

3. As an article of manufacture, a mineral fibrous mat carrying a substantially uniform continuous film on the surface of the individual fibers,.said film comprising a fused thermoplastic resin having incorporated therein a substantial amount of gelatin, said resin of a molding powder grade being a plasticized acrylic resin selected from the class consisting of methyl acrylate and methyl methacrylate.

4. An article of manufacture as claimed in claim 8 wherein the plasticizer is an acrylic resin selected from the class consisting of butyl acrylate and butyl methacrylate.

5. As an article of manufacture, a mineral fibrous mat carrying a substantially uniform continuous film on the surface of the individual fibers, said film including a binder composition consisting essentially of a fused methyl methacrylate resin having incorporated therein a substantial amount of gelatin, said resin having a polymeric growth of such degree as to provide a specific gravity of about 1.16 to 1.20 in the resin, a molding temperature of about 285 F. to 340 F., and an injection molding temperature of about 325 F. to 475 F.

6. As an article of manufacture, a mineral fibrous mat carrying a substantially uniform continuous film on the surface of the individual fibers, said film including a binder composition consisting essentially of methyl acrylate plasticized with butyl acrylate and having incorporated therein a substantial amount of gelatin, said methyl acrylate being of molding powder grade and fusible at from 250 to 475 F.

'7. In the method of manufacturing a bonded mat of mineral fibers, the step of treating the fibers witlgr a, ccmpesitic ing. powdergrade, dispersed in an aqueous solution of gelatin, volatilizingthe water to deposit the particles on the fiber surfaces while the gelatin functions throughout as a temporary binder to hold the fibers in predetermined form, and then heating to fuse the discrete particles into an adhesive film, said acrylic resinhaving the following. monomeric structure:

l l rr n coon v wherein R is a radical selected from the class consisting of hydrogen and methyl, and R is an alkyl radical selected from the class consisting of methyl,- ethyl, propyl, isopropyl, butyl, and iso--i butyl.

8. In the method of manufacturing abonded matof glass fibers, the steps of treating the fibers with a composition comprising; particles of methyl aqueous solution of to deposit the particles on the fiber surfaces while the gelatin functions throughout as porary binder to hold the fibers in predetermined form, and then heating to fuse the discrete particles into an adhesive film, said methyl methacrylate having a polymeric growth of such. de-, greevas to provide a specific gravity of about 1.16 to 1.20 in the resin, a molding temperature of about 285 F. to 340 F., and an injection mold,- ing temperature of about 325 F. to 475 9. In the method of manufacturing battery mats of bonded glass fibers, the steps of coating the fibers with, a composition comprising discrete particles of a thermoplastic acrylic resin having a molecular weight of the molding powder grade dispersed in an aqueous solution of gelatin, the

materials being present in the ratio of '75 to 90 parts by weight of acrylic resin to 10 to 25 parts by weight of gelatin, volatilizing thewater to deposit the discrete particlesof acrylic resin on the glass fiber surfaces while the gelatinfunctions as,

v .coninnsinadi c e e. partieleswofl atherm p astic.aory i -r m i Q n discrete methacrylate dispersed in an gelatin, volatilizing the water a tern following monomeric, structure:

H C O O R wherein R is a radical selected from the class consisting of hydrogen and methyl, and R. is an alkyl radical selected from the class consisting of methyl, ethyl, propyl, isopropyl, butyl, and isobutyl.

10. In the method of manufacturing a bonded; mat of fibers, the steps as claimed in claim '7 wherein concomitantly with the heating step the fibrous mass is maintained under tension whereby wrinkling is avoided.

11. In the method of manufacturing a bonded mat of glass fibers, the steps of treating the fibers with a composition comprising discrete particles of an acrylic resin selected from the class consisting of methyl acrylate and methyl methacrylate plasticized with an acrylic resin selected from the class consisting of butyl acrylate and butyl methacrylate, said particles being dispersed in an aqueous solution of gelatin; volatilizing the water to deposit the fibers on the fiber surfaces while th gelatin functions throughout as a temporary binder to hold the fibers in predetermined form; and then heating to fuse the discrete particles into an adhesive film.

12, The article of manufacture of claim 1 wherein said film comprises from to parts by weight resin and from 10 to 25 parts by weight gelatin.

THOMAS E. PHILIPPS.

References Cited in the file of this patent UNITED STATES PATENTS Number and then heating the mass from about. 

1. AS AN ARTICLE OF MANUFACTURE, A MINERAL FIBROUS MAT CARRYING A SUBSTANTIALLY UNIFORM CONTINUOUSLY FILM ON THE SURFACE OF THE INDIVIDUAL FIBERS, SAID FILM COMPRISING A FUSED THERMOPLASTIC ACRYLIC RESIN HAVING A MOLECULAR WEIGHT OF THE MOLDING POWDER GRADE AND A SUBSTANTIAL AMOUNT OF GELATIN INCORPORATED THEREIN, SAID ACRYLIC RESIN HAVING THE FOLLOWING MONOMERIC STRUCTURE: 